How to Remove an Anti-Siphon Cap on a Water Faucet

The anti-siphon or back-flow preventer on an outdoor water faucet is a safety feature. The device creates an air break in the plumbing system should a negative pressure situation occur. The importance of a properly functioning anti-siphon device is twofold. It allows the water to drain out of a garden hose accidentally left connected in freezing weather, and prevents hazardous chemicals and contaminants from entering private and municipal water systems. There are several types of caps and ways to remove them. If you cannot find the parts to repair the faucet, replace the whole unit.

Step 1

Unscrew the top of the vacuum breaker by hand; turn it to the left to remove. Only use pliers if necessary. The plastic can be broken easily.

Step 2

Pry up on one side of the cap by hand; it should pop off easily, as the lid off a shaving cream can. Try using both your thumbs to push up on the outer edge of the anti-siphon cap.

Step 3

Squeeze both sides of the cap simultaneously by hand and lift the top off. These types of caps are rare, but some do exist. They come off similarly to a pharmacy or safety medicine bottle top.

Things You Will Need

  • Screwdriver
  • Pliers


  • Only use pliers or a screwdriver if you do not have enough hand strength.


  • The cap may break if it is old and brittle.

About the Author

Kelly Schuler is both a writer and a plumber. He self published "Plumbing Do's and Dont's" in 1999. Schuler has been a licensed plumbing and gas-fitting contractor since 2001 and a licensed journeyman plumber since 1986. He actively owned and operated his own plumbing and gas fitting business from 2001 to 2008.

Photo Credits

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